Wounds in Impala During Chemical Immobilization
The impala (Aepyceros melampus)is a medium-sized antelope that inhabits the savannas of eastern and southern Africa and the bushveld regions of South Africa, and it is the most common antelope in these areas. They also tend to inhabit areas close to water sources. Impala are reddish-brown in color with a lighter underside. They have black markings on the hips and tail, white markings above each eye, under their chin and on the underside of their tails.
Impala are active during the day, with their peak being after dawn and before dusk. They are fast runners and can leap distances up to 30 feet to escape predators, and often bound as high as 10 feet) into the air over obstacles. They are also known to be very vocal; the males make loud while rutting, and all impala emit loud warning snorts if danger is present.1,2
Impala females and their young aggregate into herds consisting of between 15 and 100 individuals. They will defend their home ranges during wet seasons, but often overlap territories with other herds during the dry season. Herds of young males consisting of up to 30 individuals are also common. These are non-territorial, and during the dry season they often mix with the female herds.3 Mature, breeding males have territories that change depending on the season.
Impala are both browsers and grazers, feeding upon grasses, fruit and leaves. Impala breed between March and May, with females isolating themselves from the herd to give birth and returning once calves are born. The chief predators of impala are leopards, lions, jackals and caracal.
Chemical Immobilization and Risks
Chemical immobilization events carry inherent risks to wildlife regardless of size or species, but these risks tend to be more pronounced when dealing with larger species such as impala in the field. These risks can include such complications as capture myopathy, aspiration, dehydration, hypothermia, hyperthermia, respiratory depression and/or arrest and cardiac arrest. Many of these complications can come about as the direct result of chemical immobilization, either due to inadvertent overdose, comorbidities or latent sensitivities in individual animals.
One potential complication that may be considered less critical than others, but which must be seriously considered, is that of wounds incurred during capture events. These can happen as a result of an impala attempting to flee prior to immobilization, as it loses physical coordination during the take-down after darting.4
Physical injuries are one of the most common threats that wild animals face. In some cases, animals can incur severe injuries that kill them directly; in others, injuries can impact them in ways that are indirectly fatal (e.g., compromising their ability to find food or to evade predators). Even when an animal doesn’t die as a direct or indirect result of an injury, it can be left in a permanently compromised state or with chronic pain.5
When an impala suffers a wound during chemical immobilization, ethical imperatives dictate that those undertaking the required research or wildlife management protocols make every effort to ensure that the animal is promptly treated so that it can make as complete a recovery as is possible.
Impala and Wounds
Nearly all antelope are large hoofstock, and comparatively large as regards species typically encountered by researchers and wildlife managers in the field. Additionally, all antelope are prey animals, and have evolved with instincts and behaviors gauged to help them survive.
Consequently, impala will usually attempt to flee when approached in the field. Occasionally, this can result in injuries either before or after an animal is darted. If the approach by humans is protracted (e.g., a long vehicle or helicopter chase), the risk of complications and injury can be increased significantly. While a wide variety of injuries is possible in such circumstances, more often than not, when these occur, they are usually soft tissue injuries of varying severity.4
Antelope have developed a number of methods to deal with predators, the most noteworthy of which is their speed and agility—and impala are among the fastest and agile of the African antelopes. If an impala cannot evade its pursuer outright, it may try to hide in areas that are difficult to access.
Treating Wounds in Impala
Most injuries in impala that are connected with capture events are experienced when attempting to flee human pursuers,4and the most common injuries suffered are lacerations. While remote drug delivery via the dart itself is unlikely to result in a serious injury, darting can on occasion result in minor lacerations. In some cases, an impala may need to be immobilized specifically for the treatment of a serious wound it has suffered due to natural causes.
The first step in treatment is to clean the wound. With small, shallow lacerations, this can be done by flushing with a commercial povidone-iodine or other scrub solution. Deeper wounds can be flushed with povidone-iodine diluted with saline, and should not be sutured to allow for drainage.4 The literature recommends high volume and, ideally, high-pressure irrigation unless the tissue is very delicate. The suggested lavage volume is 50 to 100 mL of fluid per centimeter of wound. Low-pressure irrigation is gentle to tissues and does not force bacteria deeper into the wound, but this does not debride as well as high-pressure irrigation, which can be performed with a pressurized fluid bag or a large syringe with an 18-gauge catheter.5
Superficial wounds that have been cleaned should be sutured by a veterinarian. If a veterinarian is not immediately available, non-absorbable sutures should be used.
Any impala receiving a laceration prior to or during a chemical immobilization event should receive systemic antibiotics to reduce the likelihood of infection. Procaine penicillin G combined with benzathine penicillin G is a common formulation is these instances. Long-acting oxytetracycine is also frequently used to treat impala that have suffered lacerations.5,6
Considering the inherent risks associated with chemical immobilization, there is no guarantee that injuries will not occur, particularly under field conditions. However, the drug formulations currently available for immobilizing impala and other wildlife have been refined to a degree that eliminates much of the risk that existed years ago. With proper planning, safety precautions and the right drug formulations, experienced personnel can have the expectation of effective and incident-free chemical immobilization of impala in most cases.
4Kreeger T., Arnemo, J., Raath, J. Handbook of Wildlife Chemical Immobilization, International Edition, Wildlife Pharmaceuticals, Inc., Fort Collins, CO. (2002).
5vetfolio.com: Remote Injection Systems. https://www.vetfolio.com/learn/article/remote-inj...
6Friend, M., Thomas, N. J. Field Manual of Wildlife Diseases. In: Field Manual of Wildlife Diseases, United States Geological Survey, 361-368.
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